Apparatus and method for detecting a position of an actuator piston

ABSTRACT

Apparatus and method for detecting a position of an actuator piston driving a valve pin in an injection molding system. The apparatus includes an actuator housing having a body portion, surrounding an axial bore, of a substantially non-magnetic and/or magnetically permeable material, a piston, movable within the axial bore for driving a valve pin, the piston including a magnetic member generating a magnetic field such that axial movement of the piston in the bore modifies the magnetic field according to the position of the piston relative to a detection position, and a magnetic field detector attached to an exterior surface of the body portion at the detection position for detecting the magnetic field associated with the position of the piston and generating an output signal determined by the piston position.

FIELD OF THE INVENTION

The present invention relates to actuator pistons for driving valve pinsin an injection molding system, and more particularly to a system andmethod for detecting a position of a piston with a magnetic fielddetector.

BACKGROUND

Injection molding systems have been developed having flow controlmechanisms (e.g., a controller) that control the movement and/or rate ofmovement of a valve pin over the course of an injection cycle to causethe pin to move to one or select positions and/or to control the rate ofmovement of the pin over the course of the injection cycle. In oneembodiment, the pin movement is controlled in order to raise or lowerthe rate of flow of fluid material to correspond to a predeterminedprofile of fluid flow rates for the injection cycle. A sensor istypically provided that senses a condition of the fluid material or ofthe apparatus (such as pin position) and sends a signal indicative ofthe sensed condition to a program contained in a controller that usesthe signal as a variable input to control movement of the valve pin inaccordance with the predetermined profile.

SUMMARY OF THE INVENTION

The present invention relates to an apparatus and method for detecting aposition of a piston disposed within an actuator in an injection moldingsystem. In contrast to the prior art detection of a magnetic field byuse of a linear variable differential transformer (LVDT), wherein a rodextending from one end of the piston carries a ferro-magnetic core thatslides within a tube carrying the transformer coils, the presentinvention utilizes a new structural and compositional arrangement ofelements for detecting a magnetic field, and provides benefits of morereliable and robust measurement as well as a more compact arrangement ofelements.

In accordance with the invention, an actuator housing includes a bodyportion which is of a substantially non-magnetic and/or magneticallypermeable material. The body portion allows transmission of a magneticfield generated by a magnetic member embedded in a piston such thataxial movement of the piston within a bore of the non-magnetic ormagnetically permeable body portion can be detected by a magnetic fielddetector attached to an exterior surface of the body portion. In oneembodiment, the magnetic field detector is a hall effect sensor. Thesensor may comprise a portion of a hall effect circuit, mounted to theoutside of the actuator housing, for detecting changes in the magneticflux density generated by a magnetic member disposed in the piston. Whenthe piston moves, the detector measures the change in flux density andgenerates a changing output voltage. The output voltage may beprocessed, e.g., amplified and/or converted to an output current by,e.g., the hall effect circuit. The magnetic flux density can be highestat the bottom, middle, or top of the piston stroke depending on wherethe detector is placed relative to the stroke of the piston and theposition of the embedded magnetic member (magnet) in the piston. Theoutput signal of the hall effect sensor can then be used in, forexample, closed loop control applications or open loop status reporting(monitoring) applications.

In accordance with one embodiment of the invention, an apparatus isprovided for detecting a position of an actuator piston driving a valvepin in an injection molding system, the apparatus comprising:

an actuator housing having a body portion, surrounding an axial bore, ofa substantially non-magnetic and/or magnetically permeable material;

a piston, movable within the axial bore for driving a valve pin, thepiston including a magnetic member generating a magnetic field such thataxial movement of the piston in the bore modifies the magnetic fieldaccording to the position of the piston relative to a detectionposition;

a magnetic field detector attached to an exterior surface of the bodyportion at the detection position for detecting the magnetic fieldassociated with the position of the piston and generating an outputsignal determined by the piston position.

In another embodiment, the apparatus includes an electronic controllerthat processes a value indicative of the output signal to generate acontrol signal to control the piston position.

In another embodiment, the electronic controller includes a userinterface for receiving user input for adjusting the control signal tocontrol the piston position.

In another embodiment, the user interface includes operator commands forone or more modes of operation including self calibration, continuousmonitoring of pin position, and discrete determination of pin positionas opened or closed,

In another embodiment, in the self calibration mode the piston isactuated by external controls and the electronic controller converts theoutput signal(s) to position unit(s).

In another embodiment, the electronic controller receives an analogsignal from the detector for continuous monitoring of the pin position.

In another embodiment, the electronic controller includes a samplercomponent for sampling the output signal at a selected sampling rate.

In another embodiment, an electronic monitor that processes a valueindicative of the output signal for monitoring the piston position.

In another embodiment, the valve pin is driven by the piston to multiplepositions with respect to a gate.

In another embodiment, the valve pin is positionable between opened andclosed positions with respect to a gate.

In another embodiment, the detector comprises a Hall effect sensor.

In another embodiment, the detector comprises a Hall effect circuitincluding a Hall effect sensor and one or more of a power regulator,signal amplifier, current converter, and signal driver.

In another embodiment, the Hall effect sensor generates a voltage outputwhich is proportional to the displacement of the magnetic memberrelative to the sensor.

In another embodiment, the voltage output is amplified and converted toa current signal by the Hall effect circuit.

In another embodiment, the current signal is transmitted from an outputport of the Hall effect circuit to an input port of an electroniccontroller that generates a control signal based on the current signalto control the piston position.

In another embodiment, the apparatus includes a display for viewing anindicator of the pin position.

In another embodiment, the display comprises one or more of light(s);LED(s); a graph of pin position versus time; and an indicator of pinopened and pin closed.

In another embodiment, the actuator housing has a sidewall aligned withthe axial bore and the detector is mounted on the sidewall.

In another embodiment, the axial bore extends between opposing ends ofthe actuator housing and the detector is mounted on one of the opposingends.

In another embodiment, the magnetic member is located in an aperture inthe piston.

In another embodiment, the piston has an enlarged piston head and themagnetic member is located in the piston head.

In another embodiment, the actuator housing is located on a manifoldplate.

In another embodiment, the actuator housing is located in the top clampplate.

In accordance with another embodiment of the invention, in an injectionmolding system, an apparatus is provided for detection of position of apiston disposed within an actuator cylinder, the actuator cylindercomprising a wall having an interior surface surrounding and defining abore within which the piston is adapted to move to a plurality of travelpositions extending between upstream and downstream positions containedwithin the bore, the wall of the actuator cylinder having an exteriorsurface and a body extending between the interior and exterior surfaces,the apparatus comprising:

a magnetic member having a magnetic field, the magnetic member beingmounted to the piston for movement together with the piston between theupstream and downstream positions,

wherein movement of the piston modifies the magnetic field to a modifieddegree or quality that is dependent on the travel position of the pistonrelative to a detection position;

the body of the cylinder being substantially non-magnetic and/ormagnetically permeable;

a magnetic field detector mounted to the outside surface of the cylinderat the detection position wherein the body of the cylinder is disposedbetween the detection position and the magnetic member,

the detection position being disposed at a position where the magneticfield of the magnetic member is detectable by the magnetic fielddetector at all travel positions of the piston between the upstream anddownstream positions,

the magnetic field detector detecting the modified degree or quality ofthe magnetic field and generating a signal unique to each travelposition based on the detected modified degree or quality of themagnetic field,

a processor receiving the signals generated by the magnetic fielddetector, the processor using the received signals to determine thetravel position of the piston.

In another embodiment, the processor includes a triggering signal thatcan be used in providing instructions that control a drive mechanismthat drives the piston, the instructions comprising an algorithm thatuse the determined travel position of the piston to instruct the drivemechanism to drive the piston in a predetermined manner during thecourse of an injection cycle.

In another embodiment, the processor includes a triggering signal thatcan be used in providing instructions that instruct the drive mechanismto drive the piston such that the piston travels continuously upstreamfrom a gate closed position to an intermediate upstream travel positionat first travel velocity and such that the piston travels continuouslyupstream from the intermediate travel position to a predeterminedupstream position at a second travel velocity that is higher than thefirst travel velocity.

In accordance with another embodiment of the invention, a method isprovided of determining the position of a piston that is disposed withinan actuator cylinder, the actuator cylinder comprising a wall having aninterior surface surrounding and defining a bore within which the pistonis adapted to move to a plurality of travel positions extending betweenupstream and downstream positions contained within the bore, the wall ofthe actuator cylinder having an exterior surface and a body extendingbetween the interior and exterior surfaces, the method comprising;

forming the body of the cylinder from a substantially non-magneticand/or magnetically permeable material;

mounting a member that generates a magnetic field on the piston;

driving the piston together with the magnetic field generating memberwithin the bore to one or more of the travel positions;

mounting a magnetic field detector on the outside surface of thecylinder at a detection position selected to enable the detector todetect a change in a degree or quality of the magnetic field generatedby the member that generates the magnetic field;

detecting the change in degree or quality of the magnetic field with thedetector at one or more selected travel positions;

using the detected change in degree or quality of the magnetic field todetermine the travel position of the piston at one or more travelpositions between the upstream and downstream positions.

In another embodiment, the method includes using the determined travelpositions of the piston to control movement of the piston along apredetermined path of withdrawal from a gate of a mold at one or morepredetermined drive rates or one or more predetermined velocities ofwithdrawal.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and further advantages of the invention may be betterunderstood by referring to the following description in conjunction withthe accompanying drawings in which:

FIG. 1 is a schematic of one embodiment of the invention in which amagnetic member is embedded in an actuator piston and is movable withinan axial bore of an actuator housing made of a substantiallynon-magnetic and/or magnetically permeable material, and showing acontrol system for processing the output of the magnetic field detectormounted on the actuator housing;

FIG. 2 is a schematic block diagram of one embodiment of a hall effectcircuit including a hall effect sensor for detecting the magnetic field,and additional circuit components for amplifying the signal andconverting the signal to an output current signal;

FIG. 3 is a schematic cross-sectional view of one embodiment of theposition sensor mounted on an actuator housing mounted to the top plateof an injection molding system;

FIG. 4 is an enlarged cross-sectional view of the area encircled byarrow 4-4 of FIG. 3 showing the piston in the full down position;

FIG. 5 is an enlarged cross-sectional view similar to FIG. 4 showing thepiston in the full up position;

FIG. 6 is a perspective cross-sectional view of the actuator andposition sensor of FIG. 3;

FIG. 7 is a schematic view of the actuator piston and position sensor ofFIG. 6, showing the position sensor connected to a controller as in FIG.3;

FIG. 8 is a schematic diagram of one embodiment of a hall effect sensorcircuit;

FIG. 9 is a cross-sectional view of an alternative embodiment of aposition sensor mounted to an actuator housing that is mounted on a hotrunner of an injection molding system;

FIG. 10 is a schematic diagram of the magnetic field lines generated byan ideal cyclindrical magnetic member; and

FIG. 11 is a schematic illustration of a magnetic member on the pistonbeing moved relative to the hall effect sensor (HES) in variousorientations, wherein the flux density changes as the magnetic memberposition changes.

DETAILED DESCRIPTION

Various embodiments of the present invention are now described withreference to the drawings. In the following description, for purposes ofexplanation, numerous specific details are set forth in order to providea thorough understanding of one or more implementations of the presentinvention. It will be evident, however, that the present invention maybe practiced without these specific details. In other instances,well-known structures and devices are shown in block diagram form inorder to facilitate describing the present invention.

As used in this application with regard to various monitoring andcontrol systems, the terms “component” and “system” are intended torefer to a computer-related entity, either hardware, a combination ofhardware and software, software, or software in execution. For example,a component may be, but is not limited to being, a process running on aprocessor, a processor, an object, an executable, a thread of execution,a program, and/or a computer. By way of illustration, both anapplication running on a server and the server can be a component. Oneor more components may reside within a process and/or thread ofexecution and a component may be localized on one computer and/ordistributed between two or more computers.

The present invention may also be illustrated as a flow chart of aprocess of the invention. While, for the purposes of simplicity ofexplanation, the one or more methodologies shown in the form of a flowchart are described as a series of acts, it is to be understood andappreciated that the present invention is not limited by the order ofacts, as some acts may, in accordance with the present invention, occurin a different order and/or concurrent with other acts from that shownand described herein. For example, those skilled in the art willunderstand and appreciate that a methodology could alternatively berepresented as a series of interrelated states or events, such as in astate diagram. Moreover, not all illustrated acts may be required toimplement a methodology in accordance with the present invention.

In various embodiments of the invention disclosed herein, the term“data” is used. Data means any sequence of symbols (typically denoted“0” and “1”) that can be input into a computer, stored and processedthere, or transmitted to another computer. As used herein, data includesmetadata, a description of other data. Data written to storage may bedata elements of the same size, or data elements of variable sizes. Someexamples of data include information, program code, program state,program data, other data, and the like.

As used herein, computer storage media includes both volatile andnon-volatile, removable and non-removable media for storage ofinformation such as computer-readable instructions, data structures,program modules, or other data. Computer storage media includes RAM,ROM, EEPROM, FLASH memory or other memory technology, CD-ROM, digitalversatile disc (DVDs) or other optical disk storage, magnetic cassettes,magnetic tape, magnetic disk storage or other magnetic storage devices,or any other medium which can be used to store desired information andwhich can be accessed by the computer.

The methods described below may be implemented in a suitable computingand storage environment, e.g., in the context of computer-executableinstructions that may run on one or more processors, microcontrollers orother computers. In a distributed computing environment (for example)certain tasks are performed by remote processing devices that are linkedthrough a communications network and program modules may be located inboth local and remote memory storage devices. The communications networkmay include a global area network, e.g., the Internet, a local areanetwork, a wide area network or other computer network. It will beappreciated that the network connections described herein are exemplaryand other means of establishing communications between the computers maybe used.

A computer may include one or more processors and memory, e.g., aprocessing unit, a system memory, and system bus, wherein the system buscouples the system components including, but not limited to, the systemmemory and the processing unit. A computer may further include diskdrives and interfaces to external components. A variety ofcomputer-readable media can be accessed by the computer and includesboth volatile and nonvolatile media, removable and nonremovable media. Acomputer may include various user interface devices including a displayscreen, touch screen, keyboard or mouse.

FIG. 1 is a schematic diagram of a position detecting apparatus andmethod according to one embodiment of the invention. In the disclosedembodiment, a magnetic member is embedded in an actuator piston, whichis movable within an axial bore of an actuator housing made of asubstantially non-magnetic and/or magnetically permeable material. Themagnetic member generates a magnetic field such that axial movement ofthe piston in the bore modifies the magnetic field according to theposition of the piston relative to a detection position. A magneticfield sensor is attached to the exterior of the actuator housing at thedetection position, whereby the sensor detects the magnetic fieldassociated with the position of the piston and generates an outputsignal determined by the piston position. The output signal is then sentto a control system of an injection molding system, for one or more ofmonitoring and controlling the position of the piston. It is to beunderstood that the new position detector and method can be used withvarious detection circuits, molding machines and molding processes knownto those skilled in the art.

In the position detection apparatus 8 shown in FIG. 1, an actuator 10includes an actuator housing 12 and an actuator piston 22 movable in anaxial bore 14 of the housing. The piston drives a valve pin 34 of aninjection molding system; movement of the valve pin is illustrated by anarrow 35, co-axial with the movement of the piston 22 in the axial bore14 of the housing.

A magnetic member 40, here a permanent magnet 42, is embedded in thepiston sidewall 24. A magnetic field detector 50, here a hall effectsensor, is mounted on an exterior sidewall 15 of the actuator housing12. The sensor may be part of a hall effect circuit 56 (see FIG. 2)mounted on the exterior sidewall of the actuator housing. The circuithas input/output channels 57/58 for transmitting a power input signal 59from a control system 70, and a hall output signal 60 sent to thecontrol system 70.

The control system, also commonly referred to as a controller,communicates with an injection molding system for monitoring the moldingprocess. The injection molding system, one embodiment of which will bedescribed in greater detail below with respect to FIG. 3, includes amold having one or more pins each driven by an actuator for opening andclosing an opening (a mold gate) to a mold cavity. The mold may have oneor more cavities, each cavity having one or more pins. The actuator maybe any type of known actuator, including an electrical, hydraulic orpneumatic actuator. The actuator drives a valve pin for opening andclosing the gate (opening into the mold cavity), and the movement ofeach pin maybe monitored by one or more sensors or signals on/from themachine for determining one or more process parameters such as pinposition, pin velocity, or melt pressure in the cavity or in a fluidchannel upstream of the cavity (e.g., manifold), or a temperature in thecavity or in a fluid channel upstream of the cavity, or the output ofmold cycle counter. The control system may implement a recipe i.e., aset of process parameters, for controlling the molding process.

The control system may also include various operator interfaces forinputting or modifying the process parameters, testing alternativeprocess parameters, or monitoring the molding process. The controlsystem 70 of FIG. 1 is shown communicating on channel 89 with a pinopen/closed indicator panel, which may be mounted on the injectionmachine. The control system 70 also communicates via channel 88transmitting continuous position data 91 to a graphical display 92 ofpin position versus time; the display 92 may be provided on a userinterface, such as a display screen of a computer or other user inputdevice. The control system 70 may also transmit the continuous positiondata 91 to an LED indicator panel 93, in which an array of LEDsindicates to an operator the positions of one or more pins in the mold.A human operator 95 is shown interacting with the control system 70, viaone or more interfaces, for one or more processes including calibration96, continuous position monitoring 97 and opened/closed monitoring ofthe pins 98.

FIG. 2 is a more detailed schematic illustration of one embodiment of ahall effect sensor circuit that functions as the magnetic field detector50 in the apparatus of FIG. 1. The circuit 56 is mounted to or enclosedin a housing 61 and is mounted on an exterior surface of the actuatorhousing 12. The circuit includes a hall effect sensor 52 that istypically aligned radially (transverse to the lengthwise axis A of theaxial bore 14 of the housing) with or adjacent to the magnetic member 50embedded in the piston 22 so that the hall effect sensor 52 of thecircuit 56 can optimally (robustly) measure changes in the flux densityas the piston moves axially in the bore 14 of the actuator housing. Asdescribed below, there are numerous alternative relative orientations ofthe piston magnetic member and hall effect sensor which would allow thesensor to measure changes in the flux density as the piston moves in theaxial bore of the housing. The magnetic flux density will vary dependingon where the sensor 52 is placed relative to the stroke of the pistonand the position of the embedded magnetic member 50 in the piston.Although the present embodiment shows the sensor 52 mounted in/on thesidewall 15 of the actuator housing, in another embodiment the sensorcan be mounted on either end 13 a, 13 b of the actuator housing.

Returning to FIG. 2, the hall effect circuit 56 includes a powerregulator component 62 that receives power input signal 59. Theregulator adjusts the power level as necessary and sends a power signalon channel 63 to the hall effect sensor 52. The output of the halleffect sensor is a hall voltage which is transmitted on channel 64 to asignal amplifier component 65. The amplified output signal is then senton channel 66 to a current conversion and signal driver component 67which converts the hall voltage to a hall current and outputs the hallcurrent 60 to the control system 70. The communication channels betweenthe various electronic components in the hall effect circuit and otherbetween/among other components of the disclosed embodiment, can be anyknown communication media, including wired or wireless media.

FIG. 3 is an enlarged schematic view of one embodiment of the positiondetection apparatus of FIG. 1 mounted on an actuator of an injectionmolding system 5. FIG. 3 shows a portion of an injection machine with aseries of aligned plates, including a top plate 101, to which theactuator 10 is mounted, a manifold 102, and a bottom plate 103, a mold 6being secured to one surface of the bottom plate to form a mold cavity7. A central nozzle 104 is shown feeding molten material M from theinjection molding machine through a main inlet channel 105 to adistribution channel 106 of the manifold. This distribution channelcommonly feeds a plurality of separate nozzles which all commonly feedinto a common cavity 7 of the mold 6 to make one molded part. Here, justone nozzle 107 is shown feeding into the mold cavity 7 at a gate 108.During the injection cycle, molten material may be fed to one or more ofthe nozzles at one or more predetermined times, starting by opening apin 34 of a nozzle 107 and allowing the fluid material(s) M (typicallypolymer or plastic material(s)) to flow into the mold cavity. The fluidmaterial injected from the various nozzles may join together and form asingle molded part in the mold cavity 7. The relative velocity at whichthe fluid material enters into the respective nozzles is controlled bythe controller 70, and in particular embodiments by a mold recipe ortarget profile. Different types of profiles are desirable to uniformlyfill different size individual cavities associated with each nozzle, orto uniformly fill different size sections of a single cavity. A user canobserve the tracking of the actual process parameters (e.g.,temperature, pressure, position) versus the target profile during theinjection cycle in real time, or after the cycle completes.

FIG. 3 shows a hydraulic supply 110 feeding a plurality of fluidchannels 111 into the actuator for moving the piston 22 axially in thebore 14 of the actuator housing (cylinder) 12. The magnetic member is amagnet 42 mounted in/on the piston, here embedded in the piston at apredetermined location in the piston cylindrical sidewall 24, whichsidewall is slidable within the complementary cylindrical axial bore 14of the actuator housing. The piston and housing may include locatingelements (e.g., pin 17 and slot 26 shown in FIG. 6) for aligning themagnet and sensor. Here, two adjacent magnets 42 a, 42 b are radiallydisposed with respect to the hall effect sensor 52, in approximately thesame or closely adjacent planes transverse to the axis A of the bore 14of the housing 12. The body portion 18 of the housing (see FIGS. 3 and6) located between the position sensor 52 and magnet(s) 42 is made of asubstantially non-magnetic or magnetically permeable material, such asan iron-base superalloy that includes iron and one or more of nickel orits equivalent, chromium or its equivalent, aluminum or its equivalent,and typically also carbon or its equivalent. Preferably the non-magneticor magnetically permeable material comprises between about 35% and about65% by weight of iron and one or more of between about 15% and about 35%by weight of nickel, between about 5% and about 25% chromium, betweenabout 0.10% and about 1% aluminum and between about 0.01% and about0.15% carbon. The non-magnetic body portion 18 of the piston housing isused to reduce the magnetic flux interference between the magnet andsensor; in one embodiment, the entire cylindrical piston housing 12 issubstantially non-magnetic or is magnetically permeable. The output ofthe hall effect sensor circuit 60 is then fed to the controller 70, aspreviously described.

FIG. 4 is an enlarged cross-sectional view of the magnet 42, positionsensor 52, and the body portion 18 of the actuator housing between themagnet and sensor. Here, the magnet and sensor are radially aligned(transverse to axis A) and spaced apart a distance D1. The non-magneticor magnetically permeable body portion 18 of the housing transmits themagnetic field lines (see FIGS. 10-11) from the magnet 42 to the sensor52 to detect changes in the flux density as the magnet(s) 42 is/aremoved axially in the bore 14. In FIG. 4 the piston 22 is at a lowermost(full down) position, where the sensor 52 and magnet 42 are radiallyaligned.

FIG. 5 is similar to FIG. 4 but shows the piston 22 in a full upposition. Now, the magnet 42 and sensor 52 are no longer radiallyaligned, but are separated by a distance D2 at an oblique (less than90°) angle to an axis transverse to the axis A of the axial bore 14.Such movement of the piston 22 in bore 14 changes the flux densitymeasured by the sensor 52 at the sensor's axial location (the detectionposition), relative to the axial position of the magnet 42 in thepiston, the sensor 52 outputting a voltage signal which is indicative ofthe piston position in the axial bore 14. The sensor voltage output canthen be processed, e.g., amplified and/or converted to a current signal,and used in various closed loop control applications or in open loopstatus reporting applications.

FIG. 6 is a perspective cross-sectional view of the position sensor 52and actuator 10 of FIG. 3. This view shows two magnets 42 a, 42 bembedded in the cylindrical piston sidewall 24, both magnets beingmounted in a roughly radial direction transverse to the piston bore axisA, and aligned adjacent to sensor 52. The sensor 52 is mountedsubstantially in the same radial plane as the magnets. The magnets canbe moved axially up and down in the bore 14 toward or away from thesensor 52, during the molding process. The output of the sensor circuit50 is fed to the controller 70, as shown.

FIG. 7 is a schematic illustration of the piston of FIG. 6, showing tworelative orientations between the sensor 52 and magnets 42. In a firstlower piston position shown in solid lines, the two magnets 42 a, 42 bare roughly radially aligned with the sensor. In a second higherposition of the piston shown in dashed lines, the two magnets areradially offset (see arrow D1) from the sensor, and thus the fluxdensity measured by the sensor 52 will be different in the twopositions.

FIG. 8 shows schematically a circuit diagram for a hall effect circuit56 according to one embodiment of the invention. The circuit includesinput and output connectors 59/60 which communicate with a powerregulator 62. The hall effect sensor 52 produces a voltage outputindicative of the flux density which is input to the signal amplifier 67a, and then transmitted to the current converter and signal driver 67 bbefore being output to the controller 70. FIG. 8 shows one embodiment ofa hall effect circuit that can be used in the present invention. Otherembodiments are possible, which may include one or more of the same,alternative or additional components.

FIG. 9 is a cross-section view of another embodiment of an injectionmolding apparatus, wherein an actuator 10′ is mounted on the manifold102′, as opposed to on the top plate 101 as in FIG. 3. Otherwise theapparatus functions in the same way for purposes of the presentinvention. FIG. 9 shows a magnet 42 embedded in the sidewall of a pistonhead 27′, radially aligned with a hall effect sensor 52 mounted to theexterior surface of an actuator cylinder 15′. The molten material is fedfrom a distribution channel 106′ to nozzle 107′, while pin 34′ opens andcloses gate 108′ to mold cavity 7′ of mold 6′.

FIG. 10 illustrates a magnetic field of an ideal cylindrical magnet withits axisccess of symmetry inside the image plane. The magnetic field atany given point is specified by both direction and magnitude (orstrength), and thus comprises a vector field. A higher density of nearbyfield lines indicates a stronger magnetic field. The magnetic fieldpoints towards a magnet's south pole S and away from its north pole N.Permanent magnets are objects that produce their own persistent magneticfields. They are made of ferromagnetic materials, such as iron andnickel, that have been magnetized, and they have both a north pole and asouth pole.

FIG. 11, shows six different orientations of a hall effect sensor (HES)52 with respect to a piston magnet 42. The magnet can be moved relativeto the hall effect sensor in various orientations, as long as the fluxdensity changes as the magnet position changes. The orientation selectedfor a particular application would take into account the physical space,ease of output usage, and sensitivity to change desired for a particularapplication. On the left side of FIG. 11, the north-south axis of themagnet is transverse to the direction of movement D3 of the magnet, thelatter being aligned with the axis A of the bore 14 of the actuatorhousing. The sensor can be disposed adjacent either end of the magnet,near the north pole or south pole. In contrast, on the right hand sideof FIG. 11, the north-south axis of the magnet is aligned parallel withthe direction D4 of movement of the magnet. Here, the hall effect sensor52 can be mounted either at one end of the one or more magnets, offsetfrom one end of the magnets, and/or the magnets can be disposed witheither pole closer to the sensor. These and other orientations will beapparent to the skilled person.

While specific embodiments of the present invention have been shown anddescribed, it will be apparent that many modifications can be madethereto without departing from the scope of the invention. Accordingly,the invention is not limited by the foregoing description.

1. An apparatus for detecting a position of an actuator piston driving avalve pin in an injection molding system, the apparatus comprising: anactuator housing having a body portion, surrounding an axial bore, of asubstantially non-magnetic and/or magnetically permeable material; apiston, movable within the axial bore for driving a valve pin, thepiston including a magnetic member generating a magnetic field such thataxial movement of the piston in the bore modifies the magnetic fieldaccording to the position of the piston relative to a detectionposition; a magnetic field detector attached to an exterior surface ofthe body portion at the detection position for detecting the magneticfield associated with the position of the piston and generating anoutput signal determined by the piston position.
 2. The apparatus ofclaim 1, including an electronic controller that processes a valueindicative of the output signal to generate a control signal to controlthe piston position.
 3. The apparatus of claim 2, wherein the electroniccontroller includes a user interface for receiving user input foradjusting the control signal to control the piston position.
 4. Theapparatus of claim 3, wherein the user interface includes operatorcommands for one or more modes of operation including self calibration,continuous monitoring of pin position, and discrete determination of pinposition as opened or closed.
 5. The apparatus of claim 4, wherein inthe self calibration mode the piston is actuated by external controlsand the electronic controller converts the output signal(s) to positionunit(s).
 6. The apparatus of claim 2, wherein the electronic controllerreceives an analog signal from the detector for continuous monitoring ofthe pin position.
 7. The apparatus of claim 2, wherein the electroniccontroller includes a sampler component for sampling the output signalat a selected sampling rate.
 8. The apparatus of claim 1, including anelectronic monitor that processes a value indicative of the outputsignal for monitoring the piston position.
 9. The apparatus of claim 1,wherein the valve pin is driven by the piston to multiple positions withrespect to a gate.
 10. The apparatus of claim 1, wherein the valve pinis positionable between opened and closed positions with respect to agate.
 11. The apparatus of claim 1, wherein the detector comprises aHall effect sensor.
 12. The apparatus of claim 1, wherein the detectorcomprises a Hall effect circuit including a Hall effect sensor and oneor more of a power regulator, signal amplifier, current converter, andsignal driver.
 13. The apparatus of claim 12, wherein the Hall effectsensor generates a voltage output which is proportional to thedisplacement of the magnetic member relative to the sensor.
 14. Theapparatus of claim 13, wherein the voltage output is amplified andconverted to a current signal by the Hall effect circuit.
 15. Theapparatus of claim 14, wherein the current signal is transmitted from anoutput port of the Hall effect circuit to an input port of an electroniccontroller that generates a control signal based on the current signalto control the piston position.
 16. The apparatus of claim 1, furtherincluding a display for viewing an indicator of the pin position. 17.The apparatus of claim 16, wherein the display comprises one or more oflight(s); LED(s); a graph of pin position versus time; and an indicatorof pin opened and pin closed.
 18. The apparatus of claim 1, wherein theactuator housing has a sidewall aligned with the axial bore and thedetector is mounted on the sidewall.
 19. The apparatus of claim 1,wherein the axial bore extends between opposing ends of the actuatorhousing and the detector is mounted on one of the opposing ends.
 20. Theapparatus of claim 1, wherein the magnetic member is located in anaperture in the piston.
 21. The apparatus of claim 1, wherein the pistonhas an enlarged piston head and the magnetic member is located in thepiston head.
 22. The apparatus of claim 1, wherein the actuator housingis located on a manifold plate.
 23. The apparatus of claim 1, whereinthe actuator housing is located in the top clamp plate.
 24. In aninjection molding system, an apparatus for detection of position of apiston disposed within an actuator cylinder, the actuator cylindercomprising a wall having an interior surface surrounding and defining abore within which the piston is adapted to move to a plurality of travelpositions extending between upstream and downstream positions containedwithin the bore, the wall of the actuator cylinder having an exteriorsurface and a body extending between the interior and exterior surfaces,the apparatus comprising: a magnetic member having a magnetic field, themagnetic member being mounted to the piston for movement together withthe piston between the upstream and downstream positions, whereinmovement of the piston modifies the magnetic field to a modified degreeor quality that is dependent on the travel position of the pistonrelative to a detection position; the body of the cylinder beingsubstantially non-magnetic and/or magnetically permeable; a magneticfield detector mounted to the outside surface of the cylinder at thedetection position wherein the body of the cylinder is disposed betweenthe detection position and the magnetic member, the detection positionbeing disposed at a position where the magnetic field of the magneticmember is detectable by the magnetic field detector at all travelpositions of the piston between the upstream and downstream positions,the magnetic field detector detecting the modified degree or quality ofthe magnetic field and generating a signal unique to each travelposition based on the detected modified degree or quality of themagnetic field, a processor receiving the signals generated by themagnetic field detector, the processor using the received signals todetermine the travel position of the piston.
 25. The apparatus of claim24 wherein the processor includes a triggering signal that can be usedin providing instructions that control a drive mechanism that drives thepiston, the instructions comprising an algorithm that use the determinedtravel position of the piston to instruct the drive mechanism to drivethe piston in a predetermined manner during the course of an injectioncycle.
 26. The apparatus of claim 25 wherein the processor includes atriggering signal that can be used in providing instructions thatinstruct the drive mechanism to drive the piston such that the pistontravels continuously upstream from a gate closed position to anintermediate upstream travel position at first travel velocity and suchthat the piston travels continuously upstream from the intermediatetravel position to a predetermined upstream position at a second travelvelocity that is higher than the first travel velocity.
 27. Method ofdetermining the position of a piston that is disposed within an actuatorcylinder, the actuator cylinder comprising a wall having an interiorsurface surrounding and defining a bore within which the piston isadapted to move to a plurality of travel positions extending betweenupstream and downstream positions contained within the bore, the wall ofthe actuator cylinder having an exterior surface and a body extendingbetween the interior and exterior surfaces, the method comprising;forming the body of the cylinder from a substantially non-magneticand/or magnetically permeable material; mounting a member that generatesa magnetic field on the piston; driving the piston together with themagnetic field generating member within the bore to one or more of thetravel positions; mounting a magnetic field detector on the outsidesurface of the cylinder at a detection position selected to enable thedetector to detect a change in a degree or quality of the magnetic fieldgenerated by the member that generates the magnetic field; detecting thechange in degree or quality of the magnetic field with the detector atone or more selected travel positions; using the detected change indegree or quality of the magnetic field to determine the travel positionof the piston at one or more travel positions between the upstream anddownstream positions.
 28. The method of claim 27 further comprisingusing the determined travel positions of the piston to control movementof the piston along a predetermined path of withdrawal from a gate of amold at one or more predetermined drive rates or one or morepredetermined velocities of withdrawal.